1. Field of the Invention
This invention relates to a casting control system of a die cast machine, and more particularly to a casting control system wherein a high speed injection stroke of an injection plunger is automatically adjusted to provide optimum casting and the opening or closing of a breathing valve in a cavity is automatically adjusted to with a high speed injection real start position of the injection plunger.
2. Description of the Related Art
It is known that, as shown in FIG. 9, in the conventional die cast machine, an injection plunger 3 provided on a piston rod 2 of an injection cylinder 1 is advanced a full stroke S which comprises two stages including a low speed stroke SL and a high speed stroke Sh in an injection sleeve 5 connected to a mold assembly 4. Adjustment of the low speed injection stroke SL and the high speed injection stroke Sh is performed by adjusting the positional relationship between a dog 6 fixed onto a piston rod 2 and limit switches 7, 8.
In general, in a method of die casting, it is required that the injection plunger is moved at high speed by the high speed injection stroke Sh and a mold cavity is filled up with molten metal for a very short period of time, i.e. instantaneously, so that adjustment of this high speed injection stroke may greatly influence the quality of die cast products.
However, in the conventional example where the positional relationship between the dog 6 and the limit switches 7, 8 is adjusted to control the high speed injection stroke, the adjustment entirely relies on mechanical positioning, so that variable conditions of molding cannot be coped with and adjustment with high accuracy is difficult to perform, thereby lowering quality of the die cast products.
For this reason, as the result of studies and analyses, the necessity for directly and constantly controlling the high speed injection stroke in the real casting has been made clear, and the necessity for developing a system to realize this has been recognized.
Now, it is known that in die casting, gas in the mold cavity is degassed before filling the cavity with molten metal, and adjustment of timing of opening or closing of a breathing valve used for this is performed by adjusting the positional relationship between the dog and the limit switches 7, 8 and so forth.
However, the time required for the high speed injection stroke of the injection plunger is very short as aforesaid, and since this time is not much greater than an action delay time (including a relay action time) of a solenoid valve for actuating the breathing valve, the adjustment of the positional relationship between the dog 6 and the limit switches 7, 8 has been very difficult to carry out although it is very important. In consequence, when closing of the breathing valve is delayed, a possibility of blowing the molten metal out of the mold is very high, and the die cast products are lowered in quality due to a shift in timing of opening or closing of the valve.